Sigmoid

Sigmoid is a mathematical function in the shape of an S, or sigmoid curve, which normalizes data to a range between -1 and 1, so that it can be understood in terms of probabilities. Sigmoid functions are one of several activation functions used for artificial neurons.

Tanh

Tanh – pronounced “tan H” – is a hyperbolic trigonometric function, the hyperbolic tangent, which like Sigmoid serves as a transform to activate artificial neurons, among other uses. Calling tanh performs an elementwise operation on the nd-array. Its graphical representation resembles a windblown S.